Tubular Hydroid

Overview

The tubular hydroid (Ectopleura crocea) is a colonial hydrozoan cnidarian known for its distinctive, flower-like appearance. It forms dense, bushy clusters of unbranched stems that thrive in temperate coastal waters, often colonizing artificial structures.

Distribution & habitat

Native to the Atlantic coast of North America, this species has been introduced to many regions globally, including the Mediterranean, South Africa, Australia, New Zealand, and the Pacific coast of North America. It is a common fouling organism frequently found on wharf pilings, boat hulls, floating docks, and other hard substrates in subtidal zones. It prefers cold, flowing water and typically avoids soft sediments like sand or mud.

Appearance

Colonies consist of tangled masses of branching stolons that give rise to numerous unbranched, tubular stems. Each stem is encased in a rigid, often wrinkled sheath and topped with a single, striking pink-to-red hydranth. The hydranth features two whorls of tentacles: a long outer ring for capturing prey and a shorter inner ring surrounding the mouth. Between these, clusters of yellow-to-pink reproductive sporosacs are often visible.

Biology & behavior

Unlike many other hydrozoans, Ectopleura crocea lacks a free-swimming medusa stage; its reproductive cycle is entirely contained within the colony. It is a resilient species, often persisting in harbors and areas with varying water quality. The colony functions as a predator, using its tentacles to capture tiny planktonic crustaceans from the water column.